The central nervous system (CNS) site of action of the atypical benzodiazepine (BZ), Ro5 4864 (4'-chlorodiazepam), is not known. Some of the prominent CNS mediated effects of Ro5 4864 include convulsions and anxiogenic effects. Preliminary studies from our laboratory provide evidence for a novel binding site for Ro5 4864 in rat brain that is linked to a GABAA/BZ receptor and a C1- ionophore. Coupled with previous behavioral and electrophysiological evidence supporting such a link, the hypothesis that a functionally relevant and unique Ro5 4864 site located on a GABA receptor-C1- ionophore complex exists in the mammalian CNS can be proposed. The specific aims of this proposal are to characterize and determine the functional significance of this drug receptor. These aims will be accomplished by 1) in vitro characterization of binding site properties to determine if the basic criteria for receptor identification can be met; 2) evaluation of the "response" to Ro5 4864 binding site activation; 3) identification of the functional consequences of Ro5 4864 binding site activation in vivo and 4) cloning the gene(s) encoding the Ro5 4864 site. The pharmacological characterization of this GABAA receptor-C1- ionophore linked binding site may provide the framework for the development of ligands for this site that may be of therapeutic benefit in the treatment of anxiety and seizure disorders.